BD9470AEFV Datasheet, PDF (15/39 Pages) Rohm – White LED driver for medium sized and large sized LCD back light

BD9470AFM・BD9470AEFV
●The setting of REG58 capacity and shutdown procedure
VOUT discharge function is built-in this IC when IC is shutdowned, the below decribes the operation sequence.
STB
REG50
PWM
N
②
④
2.4V
STB
ON->OFF
REG58
CREG
ALL SHUTDOWN
1uS Pulse
REG58
N
DRIVER
CS
2.4V/2.5V
ALL SHUTDOWN
LED
VOUT
VOUT
ILED
LED_DRIVER
PWM=L:STOP
PWM
①
③
Figure 18.Timing chart of shutdown
○Explanation of shutdown sequence
①Set STB pin to “OFF” will stops DC/DC converter and REG58, but LED driver will remain operation.
（Reset signal is output 1uS extent to reset the latch on the IC at this time.Therefore, undershooting will be generated on
LED current, but 1uS is very short will not affect The brightness.）
②Discharge the REG58 pin voltage from 5.8V to 2.4V with −5uA current.
③The VOUT voltage will be fully discharged with ILED current and the ILED current will no longer flow.
④When REG58pin voltage will reach 2.4V (Typ.) or less to shut down all systems
○REG58 capacitance setting procedure
The shutdown time “TOFF” can be calaulated by the following equation.
T
=
C
REG
[F
]
×
3.4
[V
]
　[Sec]
OFF
5 [uA]
The longest VOUT discharge time will be obtained when the PWM duty cycle is set to the minimum VOUT.
Make REG capacitance setting with an adequate margin so that systems will be shut off after VOUT voltage is fully
discharged.
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TSZ22111・15・001
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TSZ02201-0F10C1002000-1-2
19.Oct.2013 Rev.003